Agent OS with multi‑app product: sub‑products vs feature/platform specs

[cedricfressin]

I'm wondering how to use Agent OS most effectively in case where I have a product with a shared vision and mission.
But it contains a shared backend with multiple apps (web frontend and mobile). Each apps target different platforms and therefore don't necessarily implement all the same features.
Should we set up a product system with sub-products and leverage lately introduced project_type, or simply specify one spec per feature and per platform?